School of Earth Sciences - Theses
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ItemDetection of uranium(VI) in groundwater using a field electroanalytical technique( 1999)In this thesis electroanalytical methods are investigated and a new method developed to determine uranium(VI) in groundwater samples. Differential pulse polarography, differential pulse voltammetry and adsorptive stripping voltammetry methods, with appropriate mercury drop electrodes, were optimised using the adsorptive chelate 2,5-dichloro-3,6-dihydroxy-l,4-benzoquinone (chloranilic acid). An alternative adsorptive stripping voltammetry method, with a hanging mercury drop electrode, was optimised using the chelate 8-hydroxyquinoline (oxine). The liquid mercury requirements of these techniques limit their use in the field. Therefore, mercury film electrode methods that are potentially better suited to field conditions are investigated. Chloranilic acid was found to be a suitable chelating agent for uranium determination in combination with a hanging mercury drop electrode, but the reduction of chloranilic acid was a concern. A new mercury film electrode determination method using chloranilic acid was developed but was found to result in the deterioration of the MFE to the extent of rendering the method unsuitable for uranium determination. An adsorptive stripping voltammetry, MFE method with oxine was investigated. The inability to remove the uranyl-oxine reaction products from the MFE created a memory effect that contributed to a lack of accuracy and precision when performing standard addition determinations. This interference was a significant factor in the inability to reliably measure a uranium response using an adsorptive stripping potentiometry method with oxine. The technique of square wave adsorptive stripping voltammetry with oxine in combination with a hanging mercury drop electrode was found to be the most appropriate method for uranium determination. The method was fast, sensitive, precise and accurate when analysing standard solutions. A low detection limit of 2.7 µg/L was achieved. Groundwater and surface water samples were analysed by the AdSV, HMDE method with oxine. The mineral spring water samples from Daylesford, Victoria, were high in ionic content and contained interfering ions. The unacidified samples contained high concentrations of dissolved C02 that needed to be removed prior to sample analysis to prevent pH changes during analysis. Of six unacidified samples uranium was found in only one sample, the Tipperary Spring sample at 4.9 µg/L U(VI). Interference prevented confirmation of this concentration in the acidified Tipperary Spring sample. The construction of a linear standard addition plot with a positive x-intercept was a common outcome for both the unacidified and the acidified spring samples. The uranium concentration was determined in three surface water samples collected from the Ranger Uranium Mine in the Northern Territory. Matrix interference in these surface water samples resulted in non-linearity for two standard addition determinations. A third sample was successfully analysed to give a concentration of 23 µg/L U(VI), which is in good agreement with an independent determination. The unselective nature of oxine was found to result in significant interference when analysing environmental samples by the AdSV, HMDE method with oxine. This method was found to be inappropriate for field analysis of environmental samples. However, in a laboratory environment the AdSV, HMDE method with oxine was the best performing method when determining uranium in standard solutions.
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ItemTransport, attenuation, and degradation of organic chemicals in a basaltic aquifer system near Melbourne, Australia( 1996)Groundwater in the Pliocene to Pleistocene fractured and jointed Newer Volcanics basaltic aquifer system beneath Melbourne's industrialised western suburbs is extensively contaminated by a wide variety of organic and inorganic compounds. Groundwater in Tertiary sediments underlying the Newer Volcanics is probably also contaminated by the same sources. The main objectives of this research were 1) to assess the types, concentrations, and distribution of contaminants in the Newer Volcanics aquifer system in Melbourne's western suburbs and at a selected contaminated site and 2) to determine contaminant transport, attenuation, and degradation processes affecting organic contaminants in this aquifer system. Contaminants detected in the Newer Volcanics aquifer system during this research include phenols, volatile organic compounds, polynuclear aromatic hydrocarbons, polychlorinated biphenyls, metals, and inorganic anions. The groundwater flow system in the study area comprises a single heterogeneous and anisotropic unconfined aquifer, and includes both the Newer Volcanics and underlying sedimentary units (the Brighton Group and the Werribee Formation), although hydraulic connection of these units to the volcanics is irregular. Groundwater flow in the Newer Volcanics is through vesicular and/or scoriaceous lava flow tops and bottoms, in intercalated fluvial deposits, and through the fractured and jointed lava flows. Locally (scale of less than I km square), the basaltic aquifer system may consist of hydraulically separated shallow and deep aquifer zones that are connected on a larger scale. The deep aquifer zones may be semi-confined to confined. Groundwater in the study area is recharged via throughflow from upgradient and infiltration of rainfall. Discharge from the Newer Volcanics in the study area is primarily to underlying sedimentary formations, but also to surface water features and directly to Port Phillip Bay. Several mechanisms which reduce contaminant concentrations are possible in the Newer Volcanics aquifer system. These include volatilisation, dispersion and diffusion, transient storage, matrix diffusion, sorption, hydrolysis, and biodegradation. However, the nature of porosity in the Newer Volcanics may significantly extend the lifetime of contaminant plumes via the processes of transient storage and matrix diffusion. The primary mechanisms of attenuation and degradation of organic contaminants in the Newer Volcanics aquifer system are probably biodegradation, matrix diffusion, sorption, and dispersion (for non-reactive contaminants) in order of decreasing effect. Biodegradation at the water table and discharge areas will also be significant because of atmospheric contact and increased dissolved oxygen concentrations. Because of the relative lack of organic carbon in the basaltic aquifer system, sorption will occur mainly to mineral surfaces in clay-rich zones and within the rock matrix (concurrent with matrix diffusion). In some cases, relatively undiluted contaminants may be transported along preferred flow paths to discharge locations where they may pose a potential threat to the environment prior to degradation or attenuation. It was found, at least with phenols and volatile organic compounds in groundwater at a study site, that contaminants are degraded and/or attenuated rapidly, probably via biodegradation, matrix diffusion, and sorption. Biodegradation testing of groundwater at this study site confirmed the existence of microorganisms in the aquifer system capable of aerobic degradation; indirect evidence may indicate the presence of anaerobes.